Synthetic resins including polymethyl methacrylate resins, polycarbonate resins, polystyrene resins, cyclic polyolefin resins, polyethylene terephthalate resins, and triacetyl cellulose resins have advantages including light weight, transparency and ease of working. Owing to such advantages, these synthetic resins are now utilized in a variety of articles including optical disks such as CD and DVD, display windows of liquid crystal and EL panels, and various functional films.
On use of such articles, their surface is often stained with many contaminants and marked with fingerprints. Since the adhesion of such stains and fingerprints is undesired, an appropriate surface treatment is sometimes conducted on the surface of optical data media for improving antifouling properties, reducing fingerprint receptivity or improving fingerprint removal. For example, a study has been made to carry out water-repellent or oil-repellent treatment on the surface of optical data media.
For improving the mar resistance of such media surface, it is a common practice to form a transparent, mar resistant hard coat on the writing and/or reading beam incident surface of media. The hard coat is formed by applying an actinic radiation-polymerizable/curable compound having at least two polymerizable functional groups such as (meth)acryloyl groups per molecule to the medium surface, and irradiating actinic radiation like ultraviolet radiation thereto for curing. However, since these hard coats are intended solely for mar resistance improvement, no antifouling effects with respect to dust and oil mist in the atmosphere or contaminants like fingerprints are expectable.
Known hard coats having antifouling capability to organic stains include, for example, hard coating compositions having crosslinkable fluorochemical surfactants added thereto as disclosed in JP-A 11-293159 and JP-A 2002-190136. These crosslinkable fluorochemical surfactants have polymerizable double bonds and crosslink with base resins in the hard coating compositions whereby the surfactants are fixed within the hard coats. JP-A 11-213444 and JP-A 11-503768 disclose application of fluoropolymers. However, coatings made of fluorinated material are low in strength because the fluorinated material is fixed within the coating interior as well. Reducing the amount of fluorinated material added can avoid a decline of strength at the sacrifice of antifouling property.
JP-A 2002-190136 discloses an optical data medium comprising a hard coat and a top coat of a silane coupling agent having a water or oil repellent group formed thereon, the medium having improved antifouling property on its surface. This approach is successful in imparting strength and antifouling property, but needs complex steps. It would be desirable to have a material which can impart strength and antifouling property by simply adding to a hard coat composition.